Q&A: Electropolishing and Thermal Deburring

Electropolishing

Question: I understand that electropolishing increases the fatigue resistance of metals. Where can I find supporting data on this phenomenon?

Answer: A good explanation is available in Volume 5 of the American Society of Metals Handbook, under Surface Engineering of Carbon and Alloy Steels. In there it is reported that in one instance the endurance level of a metal was increased from 1 20,000 cycles to over 10 million cycles without failure.

One explanation for the dramatically improved fatigue strength is due to removal of compressive stresses in the outer most layer of metal. The grain structure that is modified at the surface of part due to machining or grinding is known as the Bielby layer. This layer has been disturbed by a mechanical operation, is now locally work-hardened, and contains higher stress concentration levels than the bulk of the underlying metal.

In the Journal of Materials Science: Materials in Medicine Volume 16 (2005) Pages 1 07-1 1 7, the authors conclude an up to 57% increase in fatigue cycles to failure in dry service conditions on 3 1'6L SS, and up to 1 00% improvement when exposed to wet or corrosive service conditions. The authors conclude that the increase in fatigue life was attributed to reduction in surface roughness (removal of the Bielby Layer) by the electropolish process and hence a reduction in surface stress concentration levels.

Thermal Deburring

Question: What is thermal deburring?

Answer: This is a method, using thermal energy, to remove burrs and flash. Parts are placed in a furnace and a mixture of natural gas and oxygen are injected under pressure. A spark causes the mixture to ignite; forming a 6000 degree F heat wave and the thin sharp edges burst into flames and are eliminated. The main part, having a greater mass, only gets warm.